Re: [pve-devel] [PATCH qemu-server] fix #3324: clone disk: use larger blocksize for EFI disk when possible

[Stefan Reiter <s.reiter@proxmox.com>]

On 3/1/21 10:42 AM, Fabian Ebner wrote:
> Moving to Ceph is very slow when bs=1. Instead, use the biggest possible power
> of two <= 1024. At the moment our EFI image sizes are multiples of 1024, so
> just using 1024 wouldn't be a problem, but this feels more future-proof.
> 
> Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
> ---
> 
> I did not see an way for 'qemu-img dd' to use a larger blocksize while still
> specifying the exact total size if it is not a multiple of the blocksize.
>

Could it make sense to just set the block size equal to the image size 
with count=1 ? Since the images will always be very small anyway...

>   PVE/QemuServer.pm | 10 +++++++++-
>   1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
> index f401baf..e579cdf 100644
> --- a/PVE/QemuServer.pm
> +++ b/PVE/QemuServer.pm
> @@ -6991,7 +6991,15 @@ sub clone_disk {
>   		# that is given by the OVMF_VARS.fd
>   		my $src_path = PVE::Storage::path($storecfg, $drive->{file});
>   		my $dst_path = PVE::Storage::path($storecfg, $newvolid);
> -		run_command(['qemu-img', 'dd', '-n', '-O', $dst_format, "bs=1", "count=$size",
> +
> +		# Ceph doesn't like too small blocksize, see bug #3324
> +		my $bs = 1;
> +		while ($bs < $size && $bs < 1024 && $size % $bs == 0) {
> +		    $bs *= 2;
> +		}
> +		my $count = $size / $bs;
> +
> +		run_command(['qemu-img', 'dd', '-n', '-O', $dst_format, "bs=$bs", "count=$count",
>   		    "if=$src_path", "of=$dst_path"]);
>   	    } else {
>   		qemu_img_convert($drive->{file}, $newvolid, $size, $snapname, $sparseinit);
>